The invention relates to readers for reading the openings in punched document cards and more particularly to such readers utilizing radiant energy for their operation.
Conventional optical readers for document cards have generally used one light source and one light detector for each sensed position (for each row of openings in a longitudinally moveable document card) or have used fiber-optic light pipes with a single light source or with a single detector. It has also been proposed in an IBM Technical Disclosure Bulletin (Volume 17, No. 12, May, 1975, page 3684) that a plurality of light sources may be used for detecting the punched openings in a document card, using a smaller plurality of light detectors. This is accomplished using a plurality of transparent plastic blocks which have surfaces cut at 45 degrees with respect to the original directions of light transmission into the blocks so that the light is reflected in such manner as to be transmitted through a row of punched openings in a document card and is finally gathered to impinge on the smaller number of light detectors. Both the light sources and light detectors are multiplexed in order to detect individual punched openings in the document card.